1. Field of the Invention
The invention relates to transporting waste and discharging waste, such as municipal sludge waste, industrial waste, contaminated dredge sediment from coastal harbors, and other solid and liquid non-hazardous and hazardous waste, to abyssal ocean depths. In particular, the discharge of the waste at the abyssal depths takes place without contaminating the intervening water column at the discharge site.
Both of these approaches provide cost effective and environmentally safe means for the depositing/relocating of large tonnages of waste, totally isolating the waste from the intervening water column, while generating low plume, and permitting the precise emplacement of the waste in abyssal sea floor regions possessing low biodiversity, low productivity and low kinetic energy. Such regions are also amenable to long-term management/monitoring techniques.
2. Description of the Related Art
The need to dispose of waste of all kinds, such as toxic and radioactive as well as contaminated sludge, industrial waste and harbor contaminated sediments, has been met by various techniques. For example, solid waste from industrial and residential sources such as garbage, has primarily been disposed of by dumping in landfill sites and by incineration, with some recycling. Municipal waste from sludge processing facilities has also been disposed of by incineration and landfill, but the waste is often contaminated with toxins and heavy metals so that landfilling and incineration techniques are ecologically undesirable. With respect to landfill operations, toxins, pathogens and heavy metals from contaminated waste present a threat to the ground water and soil, and therefore landfill disposal of waste has recently been criticized for environmental reasons.
Attempts directed toward decreasing the pollution associated with the disposal of waste and dredge sediments have been focused on pre-treatment and post-treatment in the waste processing methods. For example, municipal waste is pre-treated to destroy pathogens and harmful bacteria, however, such processing can be expensive and is ineffective for reducing or eliminating heavy metals, for example. To reduce air pollution associated with incineration, smoke stack scrubbers are used, but such equipment is expensive to install and maintain. To protect ground water and soil contamination from landfill waste disposal, liners are being required for new and existing landfill sites in some areas. In other areas, in which the risk of ground water contamination is too great, proposed landfill sites are being rejected. Therefore, containing ground and soil contamination while still maintaining cost efficiency in the disposal method remain as problems for existing waste disposal operations, such as landfill and incineration.
Even if the threat posed to the environment can be reduced, the rate at which landfill sites are becoming filled to capacity is increasing. Recycling programs have been instituted to reduce the amount of solid waste that must be disposed of, but such programs merely slow the rate at which landfill sites are filled. With the increased sprawl of development outside major population centers, the availability of landfill sites is being reduced. Further, once a landfill has reached capacity, the land can be used for only limited purposes, especially if the landfill has been filled with contaminated waste. Therefore, the need for a viable alternative to landfill disposal of waste must be developed in order to satisfy the growing demand for environmentally safe and cost efficient waste disposal.
As an alternative to landfill and incineration methods, waste and dredge sediments have been disposed of by dumping them in the oceans and other large bodies of water. Commonly, this type of dumping involves off-loading the waste or sediments directly into the water from the surface and is referred to as top dumping. Top dumping is considered to be ecologically unsound since the dumping process and the resultant deposited waste or sediments pose a threat of contamination to the water. This contamination is sufficient to degrade marine life, and therefore such top dumping has already become unlawful in many countries, including the United States. Top dumping is currently permitted in only one EPA approved site, located in The Ferallons, approximately 40 nm (nautical miles) west of San Francisco. This site is being used for relocation of contaminated dredge sediments, at depths of approximately 10,000 feet.
It is well known in the geophysical scientific community, that there exists large abyssal sea floor regions which can be potentially used as desirable disposal sites. These sites, typically at depths greater than 11,500 feet, possess very low kinetic activity, productivity, and biodiversity. These "low-activity" zones on the ocean floor would be potentially ideal sites for the long-term isolation of large quantities of waste, in an environmentally safe manner. Additionally, they would be amenable to long-term management/monitoring techniques using prelocated instrument packages. These instrument packages would be emplaced by remotely operated deep ocean sea bed search/survey and recovery vehicles (ROVs), such as the CURV III. Suitable sites in proximity to the U.S., for example, are relatively close (&lt;800 nm) to East, West and Gulf Coast ports.
It is now being considered whether it is desirable to dispose of waste on the ocean floor at abyssal depths as an alternative to landfill disposal. In order to dispose of waste at these depths in an environmentally protected manner, it is necessary to prevent contamination of the waste with the water that supports the marine life in the shallower water column above these sites. Studies have shown that the water at abyssal depths does not readily mix with the shallower water above it, i.e. thousands of feet above it, and therefore once such waste is disposed of in the ocean at abyssal depths, it does not pose a threat to contaminating the shallower water marine life at the disposal site.
Besides municipal and industrial waste, another source of contaminated waste that presents a significant disposal problem is sediment dredged from coastal harbors (dredge spoils) that have been contaminated by nearby industries and shipping. As the level of these sediments increases in the harbors and nearby waterways, they must be dredged in order to maintain open shipping channels for harbor operations. It is estimated that of the approximate 400 million cubic yards of sediment dredge spoils removed annually from coastal harbors in the U.S., approximately 5% of the sediment is contaminated and unsuitable for direct landfill application for disposal. Accordingly, proper treatment for disposal of this type of waste is required to prevent the contamination of ground water and soil just as it is with contaminated or toxic industrial and municipal waste.
Although it is convenient to relocate dredged sediment waste for disposal in the deep ocean, top dumping of contaminated dredge spoils in the form of a high solids content loose bulk is environmentally objectionable. The previously employed approach for top dumping of this loose bulk sediment in shallow waters (18-90 meters deep) has been studied by the Army Corp of Engineer over the past twenty years, and is well understood. The process of top dumping in shallow water can be briefly described as an initial phase of high speed convective descent, a second phase of dynamic collapse of the resultant mound (this occurs within one to two minutes), a third phase of initial recolinization/passive diffusion lasting 2-6 months, and a final phase of complete biological recovery of the dump site within 9-14 months. The plume cloud generated as a result of the dumping process is at an initial concentration of approximately 750 mg/m.sup.3 and is shown to be completely settled/dissipated to concentration levels below 2-10 mg/m.sup.3 within 20-40 minutes. The effective sea floor area of the resultant mound is approximately 20 times that of the initial watch circle area one might expect if a similar dumping operation were conducted on land. Top dumping of this loose bulk sediment in abyssal depth waters, however, leads to an entirely different situation, wherein the free-fall height of the sediments is by comparison 100 times greater. One would no longer know where the sediments would fall, due to dissipative/dispersion effects of varying currents existing at different ocean depths. Additionally the plume cloud might drift for hundreds of miles. Finally, the process of long-term management/monitoring of the dumpsite would be magnified manyfold in difficulty, with comparison to top dumping in shallow water, since the mound's watch circle would be from 10 to 100 times larger in size.
As a result, it has been proposed that a dredged slurry be pumped into tanks onboard a ship and then further pumped into disposable flexible (or rigid) containers positioned in chambers once the ship arrives at the dump site. Then, bottom doors of the chambers are opened and the containers are ejected. This method is disclosed in U.K. published Patent Application GB 2,229,145 to Eriksen. Specifically, as proposed, the slurry is first transported to the dump site in tanks capable of storing a fixed volume of the slurry and then it is pumped into smaller chambers that support the filling of the flexible (or rigid) containers. Therefore, the ship's total storage capacity is effectively reduced by the size of the chambers required for the filling of the containers. Furthermore, the transport and disposal method is inefficient since the containers must be filled on site, thereby increasing the overall transport time, and adversely affecting the economic viability of the operation.
The problem with the waste disposal method proposed by Eriksen is one of magnifying manyfold, the difficulty of effecting a long-term management/monitoring capability. Although the loose bulk is contained/isolated from the intervening water column by this method, its resultant high speed descent to the sea floor is in an unguided trajectory. This trajectory is essentially random in nature, due to the cross-current effects previously discussed. If alternative means are considered to hydrodynamically slow the containers' terminal velocities, the problem is magnified even further. This is due to the increased lateral displacements that would occur, and associated uncertainty, caused by the increased time to make the descent to the abyssal sea floor.
One of the primary considerations for developing a practical waste transport and disposal operation for disposing of waste at abyssal ocean depths is economic viability. The waste must be able to be transported in sufficient volume and be able to be disposed of quickly enough at the dump site so that the operating cost for disposal and the capital investment for equipment is kept to a minimum, as compared with conventional landfill operation expenses. Efficient handling of the waste in the loading and disposal phases of the operation is critical. If a ship or barge is used for transporting the waste to the dump site, then the capacity must be adequate since the length of the round trip to the disposal site, which is typically hundreds of miles offshore, expends the greatest amount of the operation time. If the capacity is insufficient, then the transportation cost and time is increased, or the capital investment is increased in order to provide greater shipping capacity so that the disposal of waste at abyssal depths is competitive with existing landfill operations.